/Engine/Plugins/Experimental/GeometryScripting/Source/GeometryScriptingCore/Public/GeometryScript/GeometryScriptSelectionTypes.h
Call PerTriangleFunc for each TriangleID in the Selection. For Vertex Selections, Vertex one-rings are enumerated and accumulated in aTSet. For PolyGroup Selections, a full mesh iteration is used to find all Triangles in the groups.
void ProcessByTriangleID ( const [UE::Geometry::FDynamicMesh3](API\Runtime\GeometryCore\DynamicMesh\FDynamicMesh3) & Mesh, [TFunctionRef](API\Runtime\Core\GenericPlatform\TFunctionRef)< void(int32)> PerTriangleFunc, bool bProcessAllTrisIfSelectionEmpty ) const